INTERACTION OF TRIPHENYLTIN HYDRIDE AND RHODIUM - STRUCTURE OF [RH(NCBPH3)(H)(SNPH3)(PPH3)(2)] AND NMR (H-1,N-15, P-31, RH-103, SN-119) STUDY OF PYRIDINE-CONTAINING DERIVATIVES

The structure of [Rh(NCBPh3)(H)(SnPh3)(PPh3)(2)] (1) (formed from [Rh( NCBPh3)(PPh3)(3)] and Ph3SnH) was determined by a single-crystal X-ray diffraction study which shows the geometry to be equally well describ ed as a distorted tetragonal pyramid with tin at the apex or a distort ed trigonal bipyramid with a hydrogen of one of the phosphine phenyl g roups occupying the sixth coordination site. The tin-hydride distance of 2.31(5) Angstrom is consistent with a weak interaction. Crystal dat a for 1: space group, P2(1)/c; a = 12.564(4), b = 26.942(4), c = 18.00 0(3) Angstrom; beta = 92.93(2)degrees; V = 6085(2) Angstrom(3); Z = 4; R = 0.050 for 5655 reflections with I greater than or equal to 2 sigm a(I). Complex 1 reacts with pyridine and substituted pyridines L (L = pyridine (py) (a), 4-(dimethylamino)pyridine (4-Me(2)Npy) (b), and 4-c arbomethoxypyridine (CMeO(2)Cpy) (c)) in dichloromethane at -25 degree s C to give trans-[Rh(NCBPh3)(H)(SnPh3)-(PPh3)(2)(L)] (2a-c). With L = 4-Me(2)Npy, the products cis-[Rh(NCBPh3)(H)(SnPh3)(PPh3)(2)(4-Me(2)Np y)] (3) and cis- and trans-[Rh(NCBPh3)(H)(SnPh3)(PPh3)(4-Me(2)Npy)(2)] (4 and 5, respectively) are also formed. At room temperature, [Rh(NCB Ph3)(H)(SnPh3)(PPh3)(L)] (6a-c) is the final product, decomposing over a period of hours. The pyridine-containing complexes were not isolate d and were characterized by NMR spectroscopy, which showed the magnitu de of the spin coupling constant J(Sn-H) to increase by factors of up to 5.5 compared with the value of 29 Hz observed for 1. At 50 degrees C, 6 (in the presence of L and PPh3 originating from 1) undergoes redu ctive elimination of Ph3SnH to give cis-[Rh(NCBPh3)(PPh3)(2)(L)]; at t his temperature 1 is stable, decomposing only at temperatures of 85 de grees C and above. A kinetic study of the dissociation of Ph3SnH from 6b (L = 4-Me(2)Npy) gave activation parameters Delta H double dagger = 97 +/- 6 kJ mol(-1) and Delta S double dagger = 1 +/- 20 J K-1 mol(-1 ). The weakened interaction between Ph3SnH and rhodium is accounted fo r in terms of a three-center ''agostic'' bond.